Unusual 1-Alkyne Dimerization/Hydrogenation Sequences Catalyzed by [Ir(H)2(NCCH3)3(P-i-Pr3)]BF 4: Evidence for Homogeneous-Like Mechanism in Imidazolium Salts

Janeth Navarro, Mária Sági, Eduardo Sola, Fernando J. Lahoz, Isabel T. Dobrinovitch, Ágnes Kathó, Ferenc Joó, Luis A. Oro

Research output: Contribution to journalArticle

33 Citations (Scopus)

Abstract

The reaction of complex [Ir(H)2(NCCH3) 3(P-i-Pr3)]BF4 (1) with excess of 1-alkynes such as t-BuC ≡ CH and PhC ≡ CH gave the butadiene compounds Ir[η4-(R)2C4H4](NCCH 3)2(P-i-Pr3)}BF4 (R = t-Bu, 5; R = Ph, 6). Compound 5 was obtained as a single isomer containing a 1,3-disubstituted butadiene ligand, whereas 6 was formed as a 7:1 mixture of isomers containing 1,3- and 1,4-disubstituted butadienes, respectively. Spectroscopic observations showed alkenyl hydride reaction intermediates, consistent with a double insertion/C-C coupling sequence. Complexes 5 and 6 were found to react with dihydrogen to give 1 and alkenes resulting from the partial hydrogenation of the butadiene moieties. This dimerization/ hydrogenation sequence has been found to be the major reaction of t-BuC ≡ CH under conditions of homogeneous hydrogenation whereas that of PhC ≡ CH produced styrene and ethylbenzene as major products. Similar selectivity was observed for these hydrogenations using organic/ionic liquid biphasic conditions with toluene/ BMIM · BF4, suggesting reaction mechanisms similar to those operating under homogeneous conditions. This conclusion is also supported by the spectroscopic observation of alkenyl hydride intermediates during the formation of 6 in BMIM · BF4 as solvent.

Original languageEnglish
Pages (from-to)280-288
Number of pages9
JournalAdvanced Synthesis and Catalysis
Volume345
Issue number1-2
DOIs
Publication statusPublished - Jan 2003

Keywords

  • Alkynes
  • Biphasic catalysis
  • Homogeneous catalysis
  • Hydrogenation
  • Ionic liquids
  • Iridium

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry

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